H.264: How to dub audio when capturing video via component

Experts:

I'm presently successfully capturing video from various models of set-top boxes via the component video ports on the H.264. What I would like to do is dub real-time voice audio commentary onto the captured video recording by way of the two audio ports on the H.264. The idea is that when the video is played back, the voice is synchronized to the events shown on the video.

While making commentary, I would be viewing a TV connected to the STB's HDMI output (rather than the monitor window in the BM Medea Express, which seems to introduce a delay of a second or so).

I expect the physical connection would be similar to the one the H.264 documentation shows for the "Betacam SP analog deck".

I understand from earlier inquiries that I would need at least a "line converter" to condition the audio.

*** I would appreciate it if you can recommend a brand/model of line converter that would work for solution, AND recommend a suitable microphone (or type of microphone) that would connect to the converter. ***

Many thanks in advance!

-Kurt Euler

Here is a cheap mixer that would work:

http://www.bhphotovideo.com/c/product/1 ... x_A_V.html

(That mixer is battery and AC operated, but doesn't come with an AC adapter)

Cheap XLR mic:

http://www.bhphotovideo.com/c/product/2 ... VOICE.html

Don't forget you'll need an XLR cable to connect the mic to the mixer.

Thanks. I'll look into these products.

-Kurt